PCI bus running at 66 MHz?

[Morph]

I was reading this review of Promise RAID controllers and the reviewer said that performance increased significantly if you use it on a motherboard that supported running the PCI bus att 66 MHz. Actually, here's a link to the review if you want to read it, he mentions it at the end of the first block of text. Has anyone heard of this and do you know which motherboards support this? Thanks

 

[poppasp1ce]

I believe most modern motherboards have it. I thought any board with a 133MHz FSB meant it also had PCI running at half (66MHz). That's why when you overclock your FSB it can lead to video 'issues' because your also overclocking your PCI bus (and some how AGP runs through it). Though I could be wrong.

 

[Toonces311]

Most of todays motherboards have the PCI 2.1 standard which is 32bit 33mhz. If your mobo has the option of a FSB of 133, then most likely your PCI divider is at 1/4. So 133 * 1/4 =33mhz.

Now there is a new version 2.2 or 2.3? I can't remember. Anyway it is 66mhz. The Promise TX4 and TX2 can run on the 66mhz PCI bus and were designed to do it. They are also backwards compatatable and can run on the more common 33Mhz.

Don't get this confused with 64bit 33mhz pci slots. They are the ones that are longer. BTW AMD has just finished a new southbridge chip that will do 64bit 66mhz pci.

Also, I just got done setting up a Promise TX4 0+1 in a dual Tyan Thunder. I like the card. More Info

 

[bret]

isnt that on 64bit though?

 

[Peter]

PCI 2.1 specification allows 66 MHz PCI. Most mainboard chipsets in the desktop consumer area don't do that.

66 MHz PCI is electrically limited to two slots, and also requires that everything on that PCI bus is 66-MHz-capable. Hence chipsets that offer 66-MHz PCI must have two PCI busses, one fast and one slow. 64-bitness is independent of clock speed and allows mixed configurations.

Conclusion, having 66-MHz PCI requires serious extra effort on both the chipset and the mainboard.

Cards that are 66-MHz-capable will run on 33-MHz busses, and 64-bit PCI cards fit into 32-bit slots.

66-MHz and/or 64-bit cards are common in GBit-Ethernet, SCSI and RAID areas. Most PCI chips in other areas can't even do either.

regards, Peter